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What is a ERW pipe

ERW pipe (also called ERW steel pipe) is the abbreviation Electric Resistance Welded Pipes. Electric resistance welding refers to a group of welding process (including spot and seam welding) that produce coalescence of faying surfaces where heat to form the weld is generated by the electrical resistance of material combined with the time and the force used to hold the materials together during welding. ERW steel pipes and tube are available in various qualities, wall thicknesses, and diameters of the finished pipes.

As only the edges are heated, the tube possesses dean accurate surface.

Electric resistance welding can make tubes in sizes up to 0.4 metre diameter.

Tubes can also be made from steels having around 0.3% carbon.

Major factor is economy and especially in low pressure application.

Applications of ERW pipes:

ERW steel pipes are used in various engineering purposes, fencing, scaffolding, line pipes etc. It is available in lengths from single random to 120 feet depending on mill capability. What’s more, ERW steel pipes are usually used for Oil & gas pipelines, Agricultural purposes, Drinking Water for housings, in collieries for extraction of Water, Thermal Powers, Transports, Hand pumps for deep boring wells, as a strong protection for cables by Telecom Department, Structural Purposes etc. ERW steel pipe is available with square ends or beveled for welding, threaded and coupled and victaulic grooved. Surface finish of it is available in black or bare, or with protective coatings.

Production Process for ERW steel pipe:

ERW steel pipe is manufactured by rolling metal and then welding it longitudinally across its length. ERW steel pipes are welded longitudinally, manufactured from Strip / Coil and can be manufactured up to 24”OD. ERW pipe cold formed from a ribbon of steel pulled through a series of rollers and formed into a tube which is fused through a electric charge.Typical ERW tube manufacturing process of Prime Steel Pipe generally involves the following stages in a step by step procedure.

Coil Feed Ramp

The coils are removed from storage and placed on the feed ramp (see Figure 4.1). Each coil is fed into the uncoiling unit.

First Forming Section

The roll transition section receives the product from the first forming section and continues the “rounding-up” process .

Final Forming Pass Section

This section of the forming rolls finishes the rounding process and prepares the edges of the strip for welding .

High-Frequency Welder

An automatic high-frequency welder heats the edges of the strip to approximately 2600 F at the fusion point location. Pressure rollers squeeze these heated edges together to form a fusion weld.

In-Process Weld Nondestructive Inspection

Nondestructive Inspection Unit

After welding has been completed, it is inspected by independent nondestructive inspection units.

Seam Weld Normalizing

The weld area is then subjected to postweld treatment, as metallur-gically required, to remove residual welding stresses and produce a uniform normalized grain structure.

Sizing Mill

The pipe passes through a sizing mill to achieve the correct outside diamete.

Cutting the Pipe

The pipe is then cut to the correct length.

End Facing And Bevelling

This is usually stage, where the pipes ends are faced and bevelled by the end facer. All these processes are continuous with automatic arrangements. These plain ended tubes further go for processing as per the customer requirements such as galvanizing, threading, black varnishing and more.

Surface Treatment for ERW Steel Pipe

ERW steel pipe, which is short for electric resistance welded steel pipe, is widely used for low pressure liquid delivery, such as water, gas and oil field, oil drilling and machinery manufacturing, etc.Today, we’ll talk about most common seen surface treatment for electric resistance welded steel pipe.First comes fusion bond epoxy, also known as FBE coating, which is widely used to protect steel pipe used in pipeline construction from corrosion. Working temperature for FBE coated steel pipe can up from 180℃ to 250℃.Then comes varnish coating. Varnish coating is the most general surface treatment for steel pipe. General varnish coating is just an oil-liked coating on pipe surface and have strong anti-corrosion effect. For industrial steel pipes, varnish steel pipes is needed.Another surface treatment for ERW steel pipe is PE. Both PE and 3PE is common seen ways. PE coated steel pipe is widely used for liquid transportation usage pipe.Another surface treatment for ERW steel pipe is black oil coating. Black oil coating is widely used for all kinds of steel pipes. As we know, if there isn’t any surface treatment for steel pipe, it can get rust in few days in wet condition. But if we cover steel surface with black painting, it can keep well for months. And life span will expand accordingly.There are also many other surface treatment for steel pipes, such as coal tar epoxy, bitumen coating, or other coating per customer’s requirement.

Welding process of ERW pipes

Several electric resistance welding (ERW) processes are available for tube and pipe production. While each process has different characteristics, all ERW processes have one thing in common–all of them produce a forged weld.A forged weld is created by applying a combination of heat and pressure, or forging force, to the weld zone. A successful forged weld uses the optimum amount of heat, which is normally slightly less than the melting point of the material, and a nearly simultaneous application of circumferential pressure to the section, which forces the heated edges together (see Figure 1).As the name implies, the heat generated by the weld power is a result of the material’s resistance to the flow of electrical current. The pressure comes from rolls that squeeze the tube into its finished shape.The two main types of ERW are high-frequency (HF) and rotary contact wheel.

The Basics of HF Welding

The two main aspects of HF welding are processes and power supplies. Each of these can be broken down further into subcategories. Processes. The two HF welding processes are HF contact and HF induction. In both processes, the equipment that provides the electrical current is independent from the equipment that supplies the forge pressure. Also, both HF methods can employ impeders, which are soft magnetic components located inside the tube that help to focus the weld current in the strip edges.

HF Induction Welding. In the case of HF induction welding, the weld current is transmitted to the material through a work coil in front of the weld point (see Figure 2). The work coil does not contact the tube–the electrical current is induced into the material through magnetic fields that surround the tube. HF induction welding eliminates contact marks and reduces the setup required when changing tube size. It also requires less maintenance than contact welding.It is estimated that 90 percent of tube mills in North America use HF induction welding.HF Contact Welding. HF contact welding transfers weld current to the material through contacts that ride on the strip (see Figure 3). The weld power is applied directly to the tube, which makes this process more electrically efficient than HF induction welding. Because it is more efficient, it is well-suited to heavy-wall and large-diameter tube production.Power Supplies. HF welding machines also are classified by how they generate power. The two types are vacuum tube and solid-state. The vacuum tube type is the traditional power supply. Since their introduction in the early ’90s, however, solid-state units have quickly gained prominence in the industry. It is estimated that between 500 and 600 of each type are operating in North America.

The Basics of Rotary Contact Wheel Welding

In rotary contact wheel welding, the electrical current is transmitted through a contact wheel at the weld point. The contact wheel also applies some of the forge pressure necessary for the welding process.The three main types of rotary contact wheel welders are AC, DC, and square wave. In all three power supplies, electrical current is transferred by brush assemblies that engage slip rings attached to a rotating shaft that supports the contact wheels. These contact wheels transfer the current to the strip edges.AC Rotary Contact Wheel Welding. In an AC rotary contact wheel welding machine, the current is transferred through the brushes to the rotating shaft, which has a transformer mounted on it. The transformer reduces the voltage and increases the current, making it suitable for welding. The two legs of the transformer’s output circuit are connected to the two halves of the rotating contact wheel, which are insulated from each other. The strip completes the circuit by acting as a conductor between the two halves of the wheel.Traditional rotary contact wheel welders used 60-hertz AC, or common line current. A drawback to this system is that the current–and therefore the weld heat–rises and falls, limiting the speed at which the tube can be welded. An AC sine wave reaches its maximum amplitude briefly, producing weld heat that varies just as the sine wave does.

To help even out the heat variation, motor generator sets were introduced to create AC at higher frequencies. Some of the frequencies used were 180, 360, 480, and 960 Hz. A few solid-state units also were produced to generate higher-frequency currents. An AC sine wave at 960 Hz reaches its maximum amplitude 1,920 times per second, as opposed to 120 times per second with a 60-Hz signal. The 960-Hz sine wave produces heat with a much more consistent temperature.

DC Rotary Contact Wheel Welding. The next step in rotary contact wheel welding was the DC power supply. The power produced has a nearly constant amplitude. Although this solves the problem of varying heat, a major drawback is that higher maintenance costs are associated with this type of welding machine.

Because it is not possible to change the voltage of DC with a transformer, it is necessary to transmit the high-amperage, low-voltage weld current into the shaft through a large number of brushes (92 for DC versus 8 for AC) with a high current density. Transmitting high-amperage, low-voltage current produces excess (waste) heat that causes heavy wear, resulting in the high maintenance costs mentioned previously.

Square Wave Rotary Contact Wheel Welding. The latest step in the evolution of rotary contact wheel welding is the square wave power supply. This method combines the consistent weld heat of DC with the lower maintenance associated with AC units (see Figure 5). While rotary contact weld methods preceded the more commonly used HF welding processes, they still have a vital role in specialty welding applications. Rotary contact welding is useful for applications that cannot accommodate an impeder on the ID of the tube. Examples of this are small-diameter refrigeration-grade tube and tube that is painted on the ID immediately after the welding process.

How Many Roll Units Are Needed?

The types of weld pressure rolls, or squeeze boxes as they sometimes are called, that apply the pressure required for the weld are as varied as the welding units used to supply the heat. Squeeze boxes for rotary contact wheel welding typically have two or three roll units, with the contact wheel serving as one of the rolls.The number of rolls in the weld squeeze box is proportionate to the size and shape of the product being welded. There are no hard and fast rules; however, common guidelines for round tube or pipe size ranges are as follows:

3/8 to 2 in. uses two-roll units.

1/2 to 3 1/2 in. uses three-roll units.

2 to 10 in. uses four-roll units.

Larger than 10 in. uses five or more rolls.

Today, much more so than in the past, many shapes–square, rectangular, hexagonal–are welded in the finished shape rather than being reshaped after being welded round. The weld boxes used for the shapes are custom-designed for each application and usually have no more than five rolls.

Technical Requirements of ERW Steel Pipe

ERW pipes means Electric Resistance Welded Pipes. ERW steel pipes and tubes are used in various engineering purposes, fencing, scaffolding, line pipes etc. ERW steel pipes and tube are available in various qualities, wall thicknesses, and diameters of the finished pipes.

Yield strength of the N80 is higher than the J55 up to 173 ~ 206 MPa.

On the same area of ??the sample, the elongation of N80 is higher than J55.

Under the same size, the same sample orientation, the same minimum sample size, J55 grade couplings, coupling stock, coupling material, semi-finished and coupling attachment material can absorb lower than N80 steel grade.

The nondestructive testing methods of seamless pipe,coupling stock, welded tube with J55 and N80 is differeent.

J55 and N80 steel grade is not the same color: length greater than or equal 1.8m, J55 painted a bright green, N80 painted a red;

J55 chosen by the manufacturer, or organize according to the order specified length normalized (N), normalizing and tempering (N & T) or quenching and tempering (Q & T). N80 is a whole, full-length heat treatment is mandatory.

Production Technology Improving Process of ERW Pipes

Straight seam welded pipe (ERW straight seam welded steel pipe) is formed on the hot rolled plate of the forming machine, the skin effect and proximity effect of the high frequency current, melting of the pipe edge heating to the extrusion roller pressure welding to achieve production. The application of high-frequency resistance welding method in pipeline production in the 1950s has witnessed more and more mature production technology and continuous improvement of product quality in the past decade or so. First of all, in the quality of raw materials, the production of ERW steel pipe has been significantly improved, the composition of the steel design of low carbon, low P, S, micro-alloying; smelting process smelting, ladle refining, vacuum degassing, continuous casting and other new technologies In addition to the ERW controlled rolling and cold rolling process, the technology has enabled the appearance size of the hot rolled steel strips of large and medium caliber ERW steel tubes to be greatly improved in appearance quality, physical properties and chemical properties. The steel pipelines produced by Baoshan Iron and Steel Company, the highest level of hot rolled strip steel in my country, have met the American Petroleum Institute API 5L standard and are at the international advanced level. Followed by the middle and large diameter ERW molding welding and heat treatment process of the production process to achieve the computer automatic control, high frequency and computer automatic compensation system welding process heat input energy is effectively controlled to prevent welding heat input welding cold caused by low welding heat input and Excessive combustion caused by high energy. The heat treatment temperature control allows the heat treatment process to achieve the best results according to the process requirements, effectively ensuring the quality of the steel pipe welding and heat-affected zone. In addition, the progress of ERW tube straight seam welded pipe inspection technology has achieved full online or offline ultrasonic or eddy current weld risk damage, and the hydraulic pressure test may be under the supervision of a computer, stress testing and regulatory requirements. The promotion and implementation of the standard and specification APIQ1 ISO9000 series ensure the quality assurance in the whole process of production, inspection, sales and service of medium and large caliber ERW straight seam steel pipes. In recent years, various countries have been actively adopting ERW straight seam welded pipe and spiral welded pipe seamless pipe in place, in industrialized countries, ERW straight seam pipe diameter Ф610mm less, ERW steel pipe has reached about 70% of the proportion. Our production capacity of ERW Longitudinal also occasion enhanced.

ERW pipe issues and defects

ERW pipe issues and defects is related to raw materials, production methods, process conditions, equipment status and personnel. Product defects that appear in the production process by the above factors and constraints. This product defects can be divided into roughly two categories: one for product defects, that defects production of the product itself exist inconsistent sets of product standards; a class of defects generated during the production process defects, it do not form the product requirements of the standard items, but also an issue of product quality, and its trend of development will inevitably lead to product defects. Therefore, this defect is not allowed in the production process.

Process defects

No burr: burr welds. Outer burr is generally better when the watertight test water pressure. But for Ling, bending, flattening test, weld most cracking. Peach tip: weld at no glitches, and recessed within the wall, forming the tip shape of peaches, try water pressure when water-tight. But bending, flattening test, weld multiple cracking. Within the burr unilateral: watertight seam burr for the side extrusion test water pressure. Bending, flattening test, sometimes cracking. Burnt: the outer surface of small pits in the weld, welding sparks a lot of splash, the microstructure observed small holes watertight when the test water pressure, bending, flattening test, most will not crack, but the impact on the intensity of use and life expectancy.

Weld defects

Opening: straight weld plate edge face melting traces or melting traces without welding, crack two tip along the weld direction, expansion, penetrate the inner surface of the test water pressure, leaking. Crack: micro-crack crack; the outer surface of the visible appearance of fine lines, the inner surface of intact, no leakage in the test water pressure, but when crushed or cold-formed crack. Lap welding: two edge dislocation in the welding, scraping, except burrs can still see the obvious one side higher and exceed the wall thickness of the negative deviation.

Surface defects

Scratch: the general was the axis of the straight channels and scratches, deeper than the wall thickness of the negative deviation of scrap defects in the weld on both sides of a continuous nail-shaped scratch. Super wall thickness of the negative deviation. Waste big flaw. Correction hurt: the leveler spiral crushed obviously feel more than the wall thickness of the negative bias of – waste defect. Pockmarked face: the tube surface successful piece punctate small pits with a diameter of about 1mm. Warp: the pipe surface warping the separation of the part and the metal substrate into pieces, not continuous, spalling can not afford.At present, ordinary fluid on the market with the general Longitudinal Welded Pipe is generally used in high-frequency resistance welding production, which is characterized by high production efficiency, weld heat affected zone is small, low quality requirements on the bonding surface, but the molding quality requirements, forming process Any change in the shape of the V-shaped opening may cause welding quality problems.Rolling groove processing is the use of grooved joints as pipe fittings when the pipe pretreatment process. Its operating principle is the use of roll groove rolling machine driven rotating pipe, pipe radial direction of the follow-up pressure roller radial pressure applied to the use of the structure of the pressure roller welded pipe in a fixed position of cold out a specified groove.A “roll groove cracking” is the root cause of the weld strength is not enough, coupled with rolling groove processing of the severe deformation, resulting in weld stress concentration and tear. Raw material is the source of product quality, production must master its characteristics. From the welding point of view, the impact of raw materials on the quality of the weld is mainly reflected in the welding of the material and the two aspects of organization. Elements of alloying elements and the morphology of the weld quality also affect. The high content of sulfur and phosphorus in the material will easily cause crystallization segregation; the high carbon content will promote the formation of martensite, the embrittlement of the weld metal; the grain size of the metal structure is too large, the direction of the weld crystal will be strengthened; Easy to promote the segregation of impurities. There are non-metallic materials in the inclusion, stratification, width and thickness fluctuations, all kinds of factors may cause weld cracks and reduce weld strength.

ERW steel pipe main welding process parameters are input power, raw production speed, opening angle, welding pressure, induction coil (induction contact) and the location of the impedance and so on. The unreasonable setting of welding parameters is an important reason for the phenomenon of rolling groove cracking. If the input power is not enough, the speed is too fast, the input heat is insufficient, the edge of the steel strip is not completely melted, the end solid oxide can not be extruded out to form the low-temperature welding defect; conversely, the input heat is too large, , Metal splash and return inclusions and other defects. Secondly, the welding pressure is also important. If the welding pressure is not enough, the fusion line on both sides of the metal microstructure flow line is not obvious, welding strength will not meet the requirements; the other hand, the welding pressure is too large, irregular weld lines, metal flow line rise angle is too large, Reduced only when the welding pressure is appropriate should be, the fusion line without distortion, metal streamline angle of 45 °~ 60 °ideal state, the weld strength is guaranteed.

Cause Analysis of ERW Steel Pipe Surface Scratching

ERW steel pipe manufacturers, in the production of high-frequency welded pipe process, will face the tube surface was scratched the situation, the main reason for this is due to the guide roller and squeeze roller caused. The following specific analysis.

1. Scraping caused by the guide roll generally occurs on both sides of the high-frequency welded pipe, the characteristics of the wound is relatively large, continuous strong. Reasons include:

(1) The height of the guide sleeve position is not correct, such as the guide roller bearing damage, the guide roller can not be a good control of high-frequency welded pipe, so that friction with the guide sleeve caused by scratches.

(2) When the guide roll deviation from the high-frequency welded pipe production line rolling center line is too large, the guide sleeve and guide roller relative difference is too large, resulting in both sides of high-frequency welded pipe scratches.

(1) The hole does not match, resulting in ERW steel pipe surface scratches, the hole does not match the factors are: squeeze roller bearing damage, squeeze roller axial movement, squeeze roll hole size is not the same, the two extrusion Roller height position is different from the extrusion roller bending and assembly instability.

(2) Squeeze roller height does not match. The lower edge of the squeeze roll hole pattern should be consistent with the height of the rolling line, and the height of the guide roll is determined by the wall thickness of the ERW steel pipe. If the guide roller is too low, the edge of the extrusion roller hole rounded corner of the high-frequency welded pipe will cause the bottom of the scratches.

(3) Squeeze pressure on the roller is insufficient. Especially the two-roll structure of the squeeze roller device, when the pressure on the lack of ERW steel pipe tension in the role, the roller will appear on the elevation angle, the R edge of the hole prominent, resulting in high-frequency welded pipe Scratch the lower part. When the squeeze roller hole R-round grinding sharp, it will increase the scratches.

Difference Between seamless pipe and ERW pipe

Seamless pipe is a hollow cross section, no seams round, square, rectangular steel. Seamless steel ingot is made of perforated or solid tube capillary tube, and then by hot-rolled, cold-rolled or cold-call is made.Seamless hollow sections, a large number of channels for transporting fluids, steel pipe and solid steel bar, etc. compared to the same torsional strength in bending, lighter, is an economic cross-section steel, widely used in the manufacture of structural parts and mechanical parts, such as piling pipe, automotive drive shafts, bicycle frames and construction using steel scaffolding. ERW steel pipe: the high-frequency straight seam resistance welding pipes, hot-rolled wide coil as raw material, pre-bent, continuous molding, welding, heat treatment, sizing, straightening, cutting and other processes, and the spiral weld compared with the short high dimensional accuracy, uniform thickness, surface quality, the advantages of higher pressure, but the drawback is to produce only small-diameter thin-walled tube, easy to produce gray leaf spot weld, lack of fusion, groove-like corrosion defects. Currently wider application area is the city gas, crude oil transportation and so on. Mainly molding process differently. Ordinary steel, such as water pipes, generally through after bending the flat sheet by welding together, you can find a seam in the above; diameter is generally thicker welds, mainly for erw pipe. The general is seamless steel molten state through the annular slit backlog stretched out before treatment processes such as molding, so there is no seam. In performance, especially on the bearing capacity has greatly improved as compared with ordinary steel, so often used in high-voltage devices. Hydraulic equipment such as piping connections. While the ordinary steel welds is the weak link, the weld quality is also affected its overall performance of the main factors.

Diameter tolerance

ERW pipe using cold forming by 0.6% reducing sizing completed, the process temperature is almost constant at room temperature, and thus control the exact diameter range of fluctuation is small, will help eliminate black buckle; rather seamless hot-rolled Forming process, the sizing was completed around 8000C, steel raw materials, components, cooling conditions and the status of the cooling rolls have a greater impact on its outer diameter, and thus difficult to accurately control the diameter and larger range.

Exterior

Seamless steel pipe used in the outer surface of the billet hot rolling process to eliminate defects can not only after the completion of the finished, polished off defects; For left after piercing spiral track, minus the wall in the process, can only be partially eliminated. ERW steel pipe hot rolled coil as raw material, coil surface quality is ERW pipe surface quality, and ease of hot-rolled coil surface quality control and the quality is higher, therefore ERW steel pipe and seamless steel surface quality is far superior .

Tensile Test

Seamless and ERW pipe tensile performance indicators are in line with API standards, but generally at a maximum intensity seamless, plasticity is lower, comparatively speaking, ERW steel pipe strength index in the best condition, plasticity index higher than the standard 33.3% because the ERW pipe raw material – hot-rolled coil is to rely on the performance of micro-alloying smelting, refining and controlled rolling and controlled cooling and other means to ensure; seamless rely mainly on the means to increase the carbon content, it is difficult to ensure strength, ductility a reasonable match.

Nowadays, with quick construction of society and rapid development of technology, more and more different kinds of steel pipes are created, such as welded steel pipe, seamless steel pipe, ERW steel pipe and so on, and more and more steel pipes are needed. In the competitive market of steel pipe, ERW steel pipe, seamless pipe and welded steel pipe are well sold thanks to their specific characteristics.There are a few aspects of differences between ERW steel pipe and seamless steelpipe. ERW pipe, which is short for electric resistance welding, is used in delivery of liquid, such as fuel, gas and so on, regardless the requirement of pressure, which plays an important role in the conveying tube all over the world, while seamless pipe is a kind of steel pipe shaping square and rectangle and having no seam around with hollow cross-sections, which is used in conveying liquid but also making structural members and machine parts, due to its surprisingly high anti-bending and anti-torque strength and impossibly lightness. All in all, ERW pipe and seamless steel pipe is quite different in use of structural steel pipe.What’s more, the biggest difference between ERW pipe and seamless steel pipe is that ERW pipe has welding line, which is the same as welded steel pipe, but seamless black steel pipe doesn’t have, either does the welded steel pipe. Furthermore, the welding line of ERW pipe is the key to the quality of ERW steel pipe. The more unrecognizable the welding line of ERW pipe is, the higher quality ERW pipe has. As an old saying goes ‘hard work pays off’, with scientists’ continuous hard study, a huge success in eliminating the welding line of ERW pipe has been achieved. There are two ways to eliminate the welding line: geometric seamlessly and physical seamlessly. Geometric seamlessly is to eliminate the burr both inside and outside while physical seamlessly is to take steps to make base metal and metallographic structure uniform and consistent, which seems more complicate to achieve, however, a ERW pipe without a welding line can be successfully attained through which. Compared with processing technique of ERW pipe, the processing technique of seamless steel pipe is much simpler. There are two entirely different types of processing technique: cold-drawing and hot rolling. Compared with hot rolling, the technological process of cold-drawing is more complicated. Moreover, in the appearance, cold-drawn seamless stainless steel pipe is shorter than hot-rolled one and the wall thickness of cold-drawn seamless stainless steel pipe is generally smaller than the wall thickness of hot-rolled one. What’s more, the technological process of hot rolling needs high temperature which reduces the resistance of deformation so that a big deflection is achieved. Generally speaking, the technological processing of ERW pipe and seamless steel pipe are quite different, due to the different appearance.In general, although ERW pipe and seamless steel pipe both play an important role as well the welded steel pipe do in the construction of society, ERW pipe and seamless mild steel pipe has different use and different making progress thanks to their different appearance. Scientists have always been paying a lot to improve their property, which is aimed to make them more multifunctional and to reduce the cost of processing. Maybe one day, ERW pipe and seamless steel pipe will have little differences.

Seamless steel pipes are mainly used in oil pipeline and gas pipeline, but seldom used in oil pipelines with long-distance. Most long distance pipeline applied ERW pipes, SSAW pipes and LSAW pipes. Here are comparisons of technological features and performance of these pipes.

Electric Resistance Welding Pipes

Electric Resistance Welding (ERW) pipes have two kinds of welding, induction welding and contact welding. The ERW pipe applied wide hot rolling steel profile as raw material, and went through pre-bending, continuous forming, welding, straightening, cutting and other processes. The pipe has short weld joints, high dimensional accuracy, uniform thickness, and excellent surface and can bear high pressure. However, it also has shortcomings, such small diameter and thin wall, and the weld joints are easy to be eroded. Currently, ERW pipes are mainly used to transport gas as well as oil to city residents.

Spiral Submerged-Arc Welding Pipes

Spiral submerged arc welded (SSAW) pipes has spiral welding joints and the pipes are welded and formed at the same time. The strip steel with the same specification can produce SSAW pipes with various diameters. The welding joints can avoid major stress and have better force resistance. Disadvantages are poor geometrical diameters; longer welding joints and joints are easily to have cracks, porosity and other welding defects. According to the design specification of oil and gas pipeline, SSAW pipes only can be used in the third and fourth class areas. Developed countries have improved the technology, apart forming and welding, and have pre-welding and precise welding processes which make the quality of welding close to UOE pipes. Currently, the domestic market doesn’t master this technology which needs to be improved. SSAW pipes produced by traditional technique are widely used in the project of natural gas transmission from West to East China. The US, Japan and Germany believe that it’s not suitable to use SSAW pipes as main trunk; Canada and Italy use it partially and Russia use it in a small scale with strict additional condition. China, due to historical reasons, still uses SSAW pipes as main trunks in majority areas.

Longitudinally Submerged Arc Welding Pipes

Longitudinally Submerged Arc Welding (LSAW) pipes use single plate steel as raw material, applied double-sided submerged arc welding. The finished products have larger specifications and the welding joints have excellent ductility, plasticity and good sealing. LSAW pipes have large diameter, thick wall and can withstand high pressure and low temperature. LSAW pipes play a major role in oil and gas pipelines with features of high strength, high quality and long distance. According to the standard of American Petroleum Institute (API), the LSAW pipe is the only designated pipe in large scaled oil and gas transportation, especially when the pipelines cross the densely populated urban areas and the first and second class cities.

Differences between ERW steel pipe and HFW steel pipe

ERW welding process refers the heat generated by the resistance to current flow that pass through the jointed metals. So a large current is needed to electrify the whole surface of the steel plate or coil to the length of welding. In the ERW welding process, the electric current that pass through the entire conductor is at 50/60 Hz.HFW welding process is not the same case with the high-frequency process, since it’s only a section of the steel metals is heated by the induction of electric coil. High-frequency is generated by either AC or DC current. In these cases, the constant current welding generator and constant voltage high-frequency welding generator are used.Constant current welding machine generates power in 100-800 kHz. In the elder processes, the conversion of 60 Hz, AC current to HF was done by using triode and tank circuits. New welding machine uses metal oxide silicon, filed-effect transistors, usually associated with parallel resonant circuit. The constant voltage version generators use insulated gate bipolar transistors designed to power about 2000 kW with frequency rages of 100-600 KHz.

HFW is required in API 5L PSL2 ERW steel pipe

According the API 5L and ISO 3183 specification, for PSL 2 pipes in welded process the HFW welding is a mandatory requirements for ERW steel pipes. As it is an improvement from the inherent problems of hardness, lack of fusion and susceptibility of stress corrosion cracking (SCC).

ERW steel pipe includes HFW steel pipe

ERW is general designation of resistance welded steel pipes. It can be sorted into two types: alternated current welding (AC) and direct current welding (DC). According to different frequency, AC welding can be divided into low frequency welding, intermediate frequency welding, ultra frequency welding and high frequency welding. The high frequency welding (HFW) is mainly used in ordinary or thin wall steel pipe. It includes contact welding and induction welding. Direct current welding is generally used for small caliber steel tubes. In general, HFW is one of ERW production methods, it adopts the high frequency welding process. So, ERW steel pipe includes HFW steel pipe.

ERW Steel Pipe is different from UOE Steel Pipe, the difference are as follows:

1. The Raw Materials and Production Capacity Difference

The material for producing ERW Steel Pipe is hot-rolled coil or strips, while for producing UOE Steel Pipe we use hot-rolled steel. Therefore, ERW Steel Pipe can achieve a continuous pipeline operations, high production efficiency, low production costs. For UOE Steel Pipe, it can not achieve a continuous pipeline operations, low productivity, high production cost. The maximum thickness for ERW Steel Pipe can reach 25mm, and the maximum outside diameter for ERW Steel Pipe can achieve 660mm. However, the maximum wall thickness for UOE Steel Pipe is 40mm, and the maximum production outside diameter is limited by the width of the steel sheet, in current day, the maximum production outside diameter for UOE Steel Pipe is 1422mm.

2. Welding Difference

Compared with UOE Steel Pipe, one of the advantages of ERW Steel Pipe is that there is no need to have additional wire during the welding process.

3. Appearance Difference

During the production process, ERW Steel Pipe requires inside and outside welds remove, so it has a anti-corrosive advantages compared with UOE Steel Pipe.

There are some customer don’t know how to distinguish the seamless stainless steel pipe and ERW stainless steel pipe. Today, Prime Steel Pipe will discuss about differences between seamless stainless pipe and ERW stainless steel pipe.What is the raw material required for manufacturing seamless & ERW stainless steel Pipes? Seamless Steel Pipe is made from a solid round steel ‘billet’ which is heated and pushed or pulled over a form until the steel is shaped into a hollow tube. Billets are procured both from indigenous suppliers and from abroad. HR Coils are required to manufacture ERW stainless steel pipes.

How to Identify Seamless or ERW Stainless Steel pipes?

To identify that a pipe supplied is seamless or ERW, Simply read the stencil on the side of the pipe. If it is ASTM A53, Type S means seamless. Type F is furnace but welded, type E is Electrical resist welded.

What is the difference between seamless stainless steel pipe and ERW stainless steel pipe?

ERW steel pipe is manufactured by rolling metal and then welding it longitudinally across its length. Seamless pipe is manufactured by extruding the metal to the desired length; therefore ERW steel pipe have a welded joint in its cross-section, while seamless pipe does not have any joint in its cross-section through-out its length.

In Seamless steel pipe, there are no welding or joints and is manufactured from solid round billets. The seamless pipe is finished to dimensional and wall thickness specifications in sizes from 1/8 inch to 26 inch OD. Applicable in for High-pressure applications such as Hydrocarbon Industries & Refineries, Oil & Gas Exploration & Drilling, Oil & Gas Transportation and Air and Hydraulic cylinders, Bearings, Boilers, Automobiles, etc.

ERW steel pipes are welded longitudinally, manufactured from Strip / Coil and can be manufactured upto 24” OD. ERW steel pipe cold formed from a ribbon of steel pulled through a series of rollers and formed into a tube which is fused through a electric charge. It is mainly used for low/ medium pressure applications such as transportation of water / oil.

Common sizes for ERW Steel Pipe range from 2 3/8 inch OD to 24 inch OD in a variety of lengths to over 100 feet. Surface finishes are available in bare and coated formats and processing can be handled on site to customer specifications.

How to Weld for the ERW Steel Pipe in Winter

To ensure that the erw steel pipe in the winter welding perfect follow the following steps:

First, increase the welding current welding, slow down the welding speed, the appropriate increase in the cross-sectional area and length of the weld, if necessary, preheat.

Second, not outside the groove on the base metal to start arc, arc extinction to be filled when the pit.

Third, as far as possible not in low temperature conditions for bending, correction and assembly weldments.

Fourth, preheating before welding, welding process to strictly maintain the interlayer temperature should not be lower than the preheating temperature.

Fifth, the use of low hydrogen or ultra-low hydrogen welding materials.

Six, the entire weld should be finished as far as possible to avoid interruption.